Graphene-Covered Silver Nanoisland Array Coupling with Hyperbolic Metamaterials for SERS Sensing

Using metal nanoparticles as external coupling structures, electric field coupling of hyperbolic metamaterials (HMMs) to the surface has been reported as an effective way of applying HMMs to surface- enhanced Raman spectroscopy (SERS). However, for this composite structure, probe molecules cannot enter the interior of the HMM, whereas they can only accumulate on the surface and gaps of the topmost metal nanoparticles. This paper designed a graphene-covered silver nanoisland as an external coupling structure for HMMs. The flat side of this silver nanoisland faced upward. As indicated by the results, the strong electric field generated by the coupling of this hybrid system was concentrated at the top of the structure and exposed through graphene to generate a flat Raman-enhanced hot surface and conduct ultrasensitive detection. Furthermore, due to the biocompatibility of graphene, we performed Raman signal collection during the modification of DNA. The platform is promising in high-sensitivity sensors and bioassays.